A semiconductor device including an insulated-gate field-effect transistor has been widely used. Usually, such a semiconductor device is provided with an electrostatic discharge protection circuit (hereinafter, referred to as “ESD protection circuit”). The ESD protection circuit has a protection element which prevents damage due to surge current. The surge current is caused by ESD and is provided from the outside. The ESD protection circuit prevents ESD from damaging a gate insulating film of an insulated-gate field-effect transistor.
A FinFET is known as an insulated-gate field-effect transistor. The FinFET has a fin-shaped active semiconductor region. When an LSI is composed of FinFETs, a protection element of the LSI is also composed of FinFETs in practice.
JP 2007-53316, for example, discloses a protection element. The protection element has a high surge resistance for protecting a gate insulating film by employing a double-stacked structure. The protection element is provided with a plurality of gate electrodes and a plurality of gate insulating films which constitute FinFETs. The gate electrodes and the gate insulating films are stacked one after another. The double-stacked structure requires increase of the number of steps to manufacture the FinFETs of the protection element.